1. Field of the Invention
The present invention relates to a character recognition method and apparatus. More particularly, the present invention relates to a character recognition method and apparatus for extracting and recognizing characters in a motion picture.
2. Description of the Related Art
With recent improvements in image processing technology, it has become possible to extract and recognize characters in a motion picture. In addition, a technology has been developed for extracting a character area from a recognition target object that passes through a camera range and recognizing characters in the character area, in which image pickup devices and image processing apparatuses are set up in various locations indoors and/or outdoors.
For example, the character recognition apparatus can be used for a system for recognizing numbers of cars that enter a parking area to manage the cars.
FIG. 1 shows a block diagram of an example of a conventional character recognition apparatus. Each input image from an image pickup apparatus 10 is captured in a processor 20 by an image capturing part 21 every 1/30 second. For the captured image, a target object detection part 22 checks whether a recognition target object, a car, for example, appears. An image from which the recognition target object is detected is passed to a character area extraction processing part 23. The character area extraction processing part 23 extracts a character area (for example, an area of a number plate) from the recognition target object. The character recognition processing part 24 performs a matching process between the extracted character area and dictionary images, so that recognition result is output to the outside, wherein each character is compared with dictionary images to determine if there is a match in the matching process, for example.
Usually, focus and shutter speed of an infrared camera in the image pickup apparatus 10 are adjusted and fixed when the image pickup apparatus 10 is set up. After that, an iris control part 25 in the processor 20 controls, via an image pickup apparatus control part 26, an iris of the infrared camera 11 such that brightness of the character area or brightness of the whole image becomes proper for performing recognition.
However, depending on circumstances determined by location and setting conditions of the image pickup apparatus 10 and by a time period, iris control cannot be performed properly, so that characters in the image cannot be recognized accurately. For example, the iris cannot be controlled to a proper value instantaneously when shadows of surrounding objects during the daytime, irradiation from surrounding objects during the night, obstacles and the like appear.
FIG. 2 shows changes of an image of a character area due to environmental change, in which (A) corresponds to a normal condition, (B) corresponds to a condition in which shadows of surrounding objects occur during the daytime, (C) corresponds to a condition in which irradiation from surrounding objects occurs during the night, and (D) corresponds to a condition in which the character area is hidden by an obstacle. In the conditions shown in (B), (C), and (D), the character in the character area cannot be recognized properly.